Control apparatuses of this kind for a piston/cylinder arrangement are known, for example, from the press field. In this context, the term “press” is understood to be a generic term for variously functioning hydraulic presses with which it is possible to machine, in particular to shape or manufacture, a wide variety of products through the exertion of hydraulic force. Examples of such presses include hydraulic stamping presses, guillotine shears, presses for the fireproofing and tile industry, presses for manufacturing salt products, products of lime sand brick, tiles, etc. The shaping process for products can be performed in such a way that two extrusion dies, at least one of which is movable along a main axis of the press, are moved in relation to each other and thus execute the shaping procedure. In a press used in the fireproofing industry, loose bulk material, for example, is pressed into a mold by the relative movement of extrusion dies, which mold at least partially establishes the shape of the pressed item manufactured by means of the pressing procedure. By contrast with a stamping press process or guillotine shears process, the end of which is established by the completion of the stamping step or shearing procedure, the shaping procedure of the above-described press from the fireproofing industry is discontinued either when the extrusion dies have traveled a certain distance or when a certain pressure is reached in the main cylinders or when both of these criteria lie within a definite tolerance range.
Piston/cylinder arrangements that are controlled by a control apparatus of the type mentioned at the beginning are used not only for the main cylinders or main extrusion dies, but also for auxiliary functions that can also be performed by piston/cylinder arrangements controlled by the control apparatus. One such auxiliary function, for example, is the movement of a mold wall of a mold after completion of the pressing procedure in an above-introduced press from the application field of the fireproofing industry. This is the so-called demolding of the pressed item from the mold; the pressed item rests against a stationary die or main cylinder while the mold wall is moved relative to the main working axis by means of a movement produced by a piston/cylinder arrangement controlled by the control apparatus, thus removing the mold from the pressed item.
Depending on the arrangement of the auxiliary cylinder controlled by the control apparatus in relation to the press, the demolding procedure can occur as a result of an effective direction oriented in the direction of the extending or retracting piston rod of the auxiliary cylinder. Naturally, if the mold wall is kept stationary, it is also possible to demold the pressed item through a movement of a main cylinder controlled by the control apparatus.
If the control apparatus for a piston/cylinder arrangement is considered in relation to the above-described demolding of a pressed item from a mold, then the valve arrangement that is connected to the first subchamber has the known function of compensating for the own weight of the mold that is coupled, for example, to the piston of such a piston/cylinder arrangement. To that end, a pressure control value is set in the valve arrangement, which value is at least as great as the pressure in a fluid contained in the first subchamber caused by the own weight of the mold. The closing condition is therefore met (without the exertion of additional pressures), the fluid cannot flow out of the first subchamber, and the mold is therefore held in a predetermined position since the own weight is compensated for by the fluid pressure.
However, it has turned out that control apparatuses of the type described at the beginning are only satisfactory to a limited degree with regard to their durability and the durability of the piston/cylinder arrangement that they control in the usual customary technical design since after a relatively short operation time, damages occur in the components of the control apparatus itself, e.g., in position measuring systems or line systems, or damages to the piston/cylinder arrangement, e.g., the welded seams, as well as various other forms of mechanical damage. The observed, less-than-satisfactory service life of components of the control apparatus and of the piston/cylinder arrangement that it controls means that the corresponding parts have to be embodied in a reinforced way since otherwise, they have to be repaired or replaced, which is expensive, and the press may not be operational during repair work, thus resulting in production downtimes.
Attempts have been made to remedy this problem by building dampers such as hydropneumatic shock absorbers into line systems of the control apparatus. Such measures, however, have not had the desired effect.